Riedl S J, Fuentes-Prior P, Renatus M, Kairies N, Krapp S, Huber R, Salvesen G S, Bode W
Abteilung Strukturforschung, Max-Planck-Institut für Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Germany.
Proc Natl Acad Sci U S A. 2001 Dec 18;98(26):14790-5. doi: 10.1073/pnas.221580098.
Caspases form a family of proteinases required for the initiation and execution phases of apoptosis. Distinct proapoptotic stimuli lead to activation of the initiator caspases-8 and -9, which in turn activate the common executioner caspases-3 and -7 by proteolytic cleavage. Whereas crystal structures of several active caspases have been reported, no three-dimensional structure of an uncleaved caspase zymogen is available so far. We have determined the 2.9-A crystal structure of recombinant human C285A procaspase-7 and have elucidated the activation mechanism of caspases. The overall fold of the homodimeric procaspase-7 resembles that of the active tetrameric caspase-7. Each monomer is organized in two structured subdomains connected by partially flexible linkers, which asymmetrically occupy and block the central cavity, a typical feature of active caspases. This blockage is incompatible with a functional substrate binding site/active site. After proteolytic cleavage within the flexible linkers, the newly formed chain termini leave the cavity and fold outward to form stable structures. These conformational changes are associated with the formation of an intact active-site cleft. Therefore, this mechanism represents a formerly unknown type of proteinase zymogen activation.
半胱天冬酶构成了凋亡起始和执行阶段所需的一类蛋白酶。不同的促凋亡刺激会导致起始半胱天冬酶-8和-9的激活，进而通过蛋白水解切割激活共同的执行半胱天冬酶-3和-7。尽管已经报道了几种活性半胱天冬酶的晶体结构，但迄今为止尚未获得未切割的半胱天冬酶酶原的三维结构。我们确定了重组人C285A半胱天冬酶-7的2.9埃晶体结构，并阐明了半胱天冬酶的激活机制。同二聚体半胱天冬酶-7的整体折叠结构类似于活性四聚体半胱天冬酶-7。每个单体由两个结构化的亚结构域组成，通过部分柔性连接子相连，这些连接子不对称地占据并阻塞中央腔，这是活性半胱天冬酶的典型特征。这种阻塞与功能性底物结合位点/活性位点不相容。在柔性连接子内进行蛋白水解切割后，新形成的链末端离开腔并向外折叠形成稳定结构。这些构象变化与完整活性位点裂缝的形成相关。因此，这种机制代表了一种以前未知的蛋白酶酶原激活类型。
